content: /* Copyright (C) 2016-2018 Alibaba Group Holding Limited
  
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at
  
      http://www.apache.org/licenses/LICENSE-2.0
  
  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
  ==============================================================================*/
  
  // Protocol Buffers - Google's data interchange format
  // Copyright 2008 Google Inc.  All rights reserved.
  // https://developers.google.com/protocol-buffers/
  //
  // Redistribution and use in source and binary forms, with or without
  // modification, are permitted provided that the following conditions are
  // met:
  //
  //     * Redistributions of source code must retain the above copyright
  // notice, this list of conditions and the following disclaimer.
  //     * Redistributions in binary form must reproduce the above
  // copyright notice, this list of conditions and the following disclaimer
  // in the documentation and/or other materials provided with the
  // distribution.
  //     * Neither the name of Google Inc. nor the names of its
  // contributors may be used to endorse or promote products derived from
  // this software without specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  package com.google.protobuf;
  
  import java.util.AbstractMap;
  import java.util.AbstractSet;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Map;
  import java.util.NoSuchElementException;
  import java.util.Set;
  import java.util.SortedMap;
  import java.util.TreeMap;
  
  /**
   * A custom map implementation from FieldDescriptor to Object optimized to
   * minimize the number of memory allocations for instances with a small number
   * of mappings. The implementation stores the first {@code k} mappings in an
   * array for a configurable value of {@code k}, allowing direct access to the
   * corresponding {@code Entry}s without the need to create an Iterator. The
   * remaining entries are stored in an overflow map. Iteration over the entries
   * in the map should be done as follows:
   *
   * <pre>   {@code
   * for (int i = 0; i < fieldMap.getNumArrayEntries(); i++) {
   *   process(fieldMap.getArrayEntryAt(i));
   * }
   * for (Map.Entry<K, V> entry : fieldMap.getOverflowEntries()) {
   *   process(entry);
   * }
   * }</pre>
   *
   * The resulting iteration is in order of ascending field tag number. The
   * object returned by {@link #entrySet()} adheres to the same contract but is
   * less efficient as it necessarily involves creating an object for iteration.
   * <p>
   * The tradeoff for this memory efficiency is that the worst case running time
   * of the {@code put()} operation is {@code O(k + lg n)}, which happens when
   * entries are added in descending order. {@code k} should be chosen such that
   * it covers enough common cases without adversely affecting larger maps. In
   * practice, the worst case scenario does not happen for extensions because
   * extension fields are serialized and deserialized in order of ascending tag
   * number, but the worst case scenario can happen for DynamicMessages.
   * <p>
   * The running time for all other operations is similar to that of
   * {@code TreeMap}.
   * <p>
   * Instances are not thread-safe until {@link #makeImmutable()} is called,
   * after which any modifying operation will result in an
   * {@link UnsupportedOperationException}.
   *
   * @author darick@google.com Darick Tong
   */
  // This class is final for all intents and purposes because the constructor is
  // private. However, the FieldDescriptor-specific logic is encapsulated in
  // a subclass to aid testability of the core logic.
  class SmallSortedMap<K extends Comparable<K>, V> extends AbstractMap<K, V> {
  
    /**
     * Creates a new instance for mapping FieldDescriptors to their values.
     * The {@link #makeImmutable()} implementation will convert the List values
     * of any repeated fields to unmodifiable lists.
     *
     * @param arraySize The size of the entry array containing the
     *        lexicographically smallest mappings.
     */
    static <FieldDescriptorType extends
        FieldSet.FieldDescriptorLite<FieldDescriptorType>>
        SmallSortedMap<FieldDescriptorType, Object> newFieldMap(int arraySize) {
      return new SmallSortedMap<FieldDescriptorType, Object>(arraySize) {
        @Override
        @SuppressWarnings("unchecked")
        public void makeImmutable() {
          if (!isImmutable()) {
            for (int i = 0; i < getNumArrayEntries(); i++) {
              final Map.Entry<FieldDescriptorType, Object> entry =
                  getArrayEntryAt(i);
              if (entry.getKey().isRepeated()) {
                final List value = (List) entry.getValue();
                entry.setValue(Collections.unmodifiableList(value));
              }
            }
            for (Map.Entry<FieldDescriptorType, Object> entry :
                     getOverflowEntries()) {
              if (entry.getKey().isRepeated()) {
                final List value = (List) entry.getValue();
                entry.setValue(Collections.unmodifiableList(value));
              }
            }
          }
          super.makeImmutable();
        }
      };
    }
  
    /**
     * Creates a new instance for testing.
     *
     * @param arraySize The size of the entry array containing the
     *        lexicographically smallest mappings.
     */
    static <K extends Comparable<K>, V> SmallSortedMap<K, V> newInstanceForTest(
        int arraySize) {
      return new SmallSortedMap<K, V>(arraySize);
    }
  
    private final int maxArraySize;
    // The "entry array" is actually a List because generic arrays are not
    // allowed. ArrayList also nicely handles the entry shifting on inserts and
    // removes.
    private List<Entry> entryList;
    private Map<K, V> overflowEntries;
    private boolean isImmutable;
    // The EntrySet is a stateless view of the Map. It's initialized the first
    // time it is requested and reused henceforth.
    private volatile EntrySet lazyEntrySet;
  
    /**
     * @code arraySize Size of the array in which the lexicographically smallest
     *       mappings are stored. (i.e. the {@code k} referred to in the class
     *       documentation).
     */
    private SmallSortedMap(int arraySize) {
      this.maxArraySize = arraySize;
      this.entryList = Collections.emptyList();
      this.overflowEntries = Collections.emptyMap();
    }
  
    /** Make this map immutable from this point forward. */
    public void makeImmutable() {
      if (!isImmutable) {
        // Note: There's no need to wrap the entryList in an unmodifiableList
        // because none of the list's accessors are exposed. The iterator() of
        // overflowEntries, on the other hand, is exposed so it must be made
        // unmodifiable.
        overflowEntries = overflowEntries.isEmpty() ?
            Collections.<K, V>emptyMap() :
            Collections.unmodifiableMap(overflowEntries);
        isImmutable = true;
      }
    }
  
    /** @return Whether {@link #makeImmutable()} has been called. */
    public boolean isImmutable() {
      return isImmutable;
    }
  
    /** @return The number of entries in the entry array. */
    public int getNumArrayEntries() {
      return entryList.size();
    }
  
    /** @return The array entry at the given {@code index}. */
    public Map.Entry<K, V> getArrayEntryAt(int index) {
      return entryList.get(index);
    }
  
    /** @return There number of overflow entries. */
    public int getNumOverflowEntries() {
      return overflowEntries.size();
    }
  
    /** @return An iterable over the overflow entries. */
    public Iterable<Map.Entry<K, V>> getOverflowEntries() {
      return overflowEntries.isEmpty() ?
          EmptySet.<Map.Entry<K, V>>iterable() :
          overflowEntries.entrySet();
    }
  
  
    @Override
    public int size() {
      return entryList.size() + overflowEntries.size();
    }
  
    /**
     * The implementation throws a {@code ClassCastException} if o is not an
     * object of type {@code K}.
     *
     * {@inheritDoc}
     */
    @Override
    public boolean containsKey(Object o) {
      @SuppressWarnings("unchecked")
      final K key = (K) o;
      return binarySearchInArray(key) >= 0 || overflowEntries.containsKey(key);
    }
  
    /**
     * The implementation throws a {@code ClassCastException} if o is not an
     * object of type {@code K}.
     *
     * {@inheritDoc}
     */
    @Override
    public V get(Object o) {
      @SuppressWarnings("unchecked")
      final K key = (K) o;
      final int index = binarySearchInArray(key);
      if (index >= 0) {
        return entryList.get(index).getValue();
      }
      return overflowEntries.get(key);
    }
  
    @Override
    public V put(K key, V value) {
      checkMutable();
      final int index = binarySearchInArray(key);
      if (index >= 0) {
        // Replace existing array entry.
        return entryList.get(index).setValue(value);
      }
      ensureEntryArrayMutable();
      final int insertionPoint = -(index + 1);
      if (insertionPoint >= maxArraySize) {
        // Put directly in overflow.
        return getOverflowEntriesMutable().put(key, value);
      }
      // Insert new Entry in array.
      if (entryList.size() == maxArraySize) {
        // Shift the last array entry into overflow.
        final Entry lastEntryInArray = entryList.remove(maxArraySize - 1);
        getOverflowEntriesMutable().put(lastEntryInArray.getKey(),
                                        lastEntryInArray.getValue());
      }
      entryList.add(insertionPoint, new Entry(key, value));
      return null;
    }
  
    @Override
    public void clear() {
      checkMutable();
      if (!entryList.isEmpty()) {
        entryList.clear();
      }
      if (!overflowEntries.isEmpty()) {
        overflowEntries.clear();
      }
    }
  
    /**
     * The implementation throws a {@code ClassCastException} if o is not an
     * object of type {@code K}.
     *
     * {@inheritDoc}
     */
    @Override
    public V remove(Object o) {
      checkMutable();
      @SuppressWarnings("unchecked")
      final K key = (K) o;
      final int index = binarySearchInArray(key);
      if (index >= 0) {
        return removeArrayEntryAt(index);
      }
      // overflowEntries might be Collections.unmodifiableMap(), so only
      // call remove() if it is non-empty.
      if (overflowEntries.isEmpty()) {
        return null;
      } else {
        return overflowEntries.remove(key);
      }
    }
  
    private V removeArrayEntryAt(int index) {
      checkMutable();
      final V removed = entryList.remove(index).getValue();
      if (!overflowEntries.isEmpty()) {
        // Shift the first entry in the overflow to be the last entry in the
        // array.
        final Iterator<Map.Entry<K, V>> iterator =
            getOverflowEntriesMutable().entrySet().iterator();
        entryList.add(new Entry(iterator.next()));
        iterator.remove();
      }
      return removed;
    }
  
    /**
     * @param key The key to find in the entry array.
     * @return The returned integer position follows the same semantics as the
     *     value returned by {@link java.util.Arrays#binarySearch()}.
     */
    private int binarySearchInArray(K key) {
      int left = 0;
      int right = entryList.size() - 1;
  
      // Optimization: For the common case in which entries are added in
      // ascending tag order, check the largest element in the array before
      // doing a full binary search.
      if (right >= 0) {
        int cmp = key.compareTo(entryList.get(right).getKey());
        if (cmp > 0) {
          return -(right + 2);  // Insert point is after "right".
        } else if (cmp == 0) {
          return right;
        }
      }
  
      while (left <= right) {
        int mid = (left + right) / 2;
        int cmp = key.compareTo(entryList.get(mid).getKey());
        if (cmp < 0) {
          right = mid - 1;
        } else if (cmp > 0) {
          left = mid + 1;
        } else {
          return mid;
        }
      }
      return -(left + 1);
    }
  
    /**
     * Similar to the AbstractMap implementation of {@code keySet()} and
     * {@code values()}, the entry set is created the first time this method is
     * called, and returned in response to all subsequent calls.
     *
     * {@inheritDoc}
     */
    @Override
    public Set<Map.Entry<K, V>> entrySet() {
      if (lazyEntrySet == null) {
        lazyEntrySet = new EntrySet();
      }
      return lazyEntrySet;
    }
  
  
    /**
     * @throws UnsupportedOperationException if {@link #makeImmutable()} has
     *         has been called.
     */
    private void checkMutable() {
      if (isImmutable) {
        throw new UnsupportedOperationException();
      }
    }
  
    /**
     * @return a {@link SortedMap} to which overflow entries mappings can be
     *         added or removed.
     * @throws UnsupportedOperationException if {@link #makeImmutable()} has been
     *         called.
     */
    @SuppressWarnings("unchecked")
    private SortedMap<K, V> getOverflowEntriesMutable() {
      checkMutable();
      if (overflowEntries.isEmpty() && !(overflowEntries instanceof TreeMap)) {
        overflowEntries = new TreeMap<K, V>();
      }
      return (SortedMap<K, V>) overflowEntries;
    }
  
    /**
     * Lazily creates the entry list. Any code that adds to the list must first
     * call this method.
     */
    private void ensureEntryArrayMutable() {
      checkMutable();
      if (entryList.isEmpty() && !(entryList instanceof ArrayList)) {
        entryList = new ArrayList<Entry>(maxArraySize);
      }
    }
  
    /**
     * Entry implementation that implements Comparable in order to support
     * binary search within the entry array. Also checks mutability in
     * {@link #setValue()}.
     */
    private class Entry implements Map.Entry<K, V>, Comparable<Entry> {
  
      private final K key;
      private V value;
  
      Entry(Map.Entry<K, V> copy) {
        this(copy.getKey(), copy.getValue());
      }
  
      Entry(K key, V value) {
        this.key = key;
        this.value = value;
      }
  
      @Override
      public K getKey() {
        return key;
      }
  
      @Override
      public V getValue() {
        return value;
      }
  
      @Override
      public int compareTo(Entry other) {
        return getKey().compareTo(other.getKey());
      }
  
      @Override
      public V setValue(V newValue) {
        checkMutable();
        final V oldValue = this.value;
        this.value = newValue;
        return oldValue;
      }
  
      @Override
      public boolean equals(Object o) {
        if (o == this) {
          return true;
        }
        if (!(o instanceof Map.Entry)) {
          return false;
        }
        @SuppressWarnings("unchecked")
        Map.Entry<?, ?> other = (Map.Entry<?, ?>) o;
        return equals(key, other.getKey()) && equals(value, other.getValue());
      }
  
      @Override
      public int hashCode() {
        return (key == null ? 0 : key.hashCode()) ^
            (value == null ? 0 : value.hashCode());
      }
  
      @Override
      public String toString() {
        return key + "=" + value;
      }
  
      /** equals() that handles null values. */
      private boolean equals(Object o1, Object o2) {
        return o1 == null ? o2 == null : o1.equals(o2);
      }
    }
  
    /**
     * Stateless view of the entries in the field map.
     */
    private class EntrySet extends AbstractSet<Map.Entry<K, V>> {
  
      @Override
      public Iterator<Map.Entry<K, V>> iterator() {
        return new EntryIterator();
      }
  
      @Override
      public int size() {
        return SmallSortedMap.this.size();
      }
  
      /**
       * Throws a {@link ClassCastException} if o is not of the expected type.
       *
       * {@inheritDoc}
       */
      @Override
      public boolean contains(Object o) {
        @SuppressWarnings("unchecked")
        final Map.Entry<K, V> entry = (Map.Entry<K, V>) o;
        final V existing = get(entry.getKey());
        final V value = entry.getValue();
        return existing == value ||
            (existing != null && existing.equals(value));
      }
  
      @Override
      public boolean add(Map.Entry<K, V> entry) {
        if (!contains(entry)) {
          put(entry.getKey(), entry.getValue());
          return true;
        }
        return false;
      }
  
      /**
       * Throws a {@link ClassCastException} if o is not of the expected type.
       *
       * {@inheritDoc}
       */
      @Override
      public boolean remove(Object o) {
        @SuppressWarnings("unchecked")
        final Map.Entry<K, V> entry = (Map.Entry<K, V>) o;
        if (contains(entry)) {
          SmallSortedMap.this.remove(entry.getKey());
          return true;
        }
        return false;
      }
  
      @Override
      public void clear() {
        SmallSortedMap.this.clear();
      }
    }
  
  
    /**
     * Iterator implementation that switches from the entry array to the overflow
     * entries appropriately.
     */
    private class EntryIterator implements Iterator<Map.Entry<K, V>> {
  
      private int pos = -1;
      private boolean nextCalledBeforeRemove;
      private Iterator<Map.Entry<K, V>> lazyOverflowIterator;
  
      @Override
      public boolean hasNext() {
        return (pos + 1) < entryList.size()
            || (!overflowEntries.isEmpty() && getOverflowIterator().hasNext());
      }
  
      @Override
      public Map.Entry<K, V> next() {
        nextCalledBeforeRemove = true;
        // Always increment pos so that we know whether the last returned value
        // was from the array or from overflow.
        if (++pos < entryList.size()) {
          return entryList.get(pos);
        }
        return getOverflowIterator().next();
      }
  
      @Override
      public void remove() {
        if (!nextCalledBeforeRemove) {
          throw new IllegalStateException("remove() was called before next()");
        }
        nextCalledBeforeRemove = false;
        checkMutable();
  
        if (pos < entryList.size()) {
          removeArrayEntryAt(pos--);
        } else {
          getOverflowIterator().remove();
        }
      }
  
      /**
       * It is important to create the overflow iterator only after the array
       * entries have been iterated over because the overflow entry set changes
       * when the client calls remove() on the array entries, which invalidates
       * any existing iterators.
       */
      private Iterator<Map.Entry<K, V>> getOverflowIterator() {
        if (lazyOverflowIterator == null) {
          lazyOverflowIterator = overflowEntries.entrySet().iterator();
        }
        return lazyOverflowIterator;
      }
    }
  
    /**
     * Helper class that holds immutable instances of an Iterable/Iterator that
     * we return when the overflow entries is empty. This eliminates the creation
     * of an Iterator object when there is nothing to iterate over.
     */
    private static class EmptySet {
  
      private static final Iterator<Object> ITERATOR =
          new Iterator<Object>() {
            @Override
            public boolean hasNext() {
              return false;
            }
            @Override
            public Object next() {
              throw new NoSuchElementException();
            }
            @Override
            public void remove() {
              throw new UnsupportedOperationException();
            }
          };
  
      private static final Iterable<Object> ITERABLE =
          new Iterable<Object>() {
            @Override
            public Iterator<Object> iterator() {
              return ITERATOR;
            }
          };
  
      @SuppressWarnings("unchecked")
      static <T> Iterable<T> iterable() {
        return (Iterable<T>) ITERABLE;
      }
    }
  
    @Override
    public boolean equals(Object o) {
      if (this == o) {
        return true;
      }
  
      if (!(o instanceof SmallSortedMap)) {
        return super.equals(o);
      }
  
      SmallSortedMap<?, ?> other = (SmallSortedMap<?, ?>) o;
      final int size = size();
      if (size != other.size()) {
        return false;
      }
  
      // Best effort try to avoid allocating an entry set.
      final int numArrayEntries = getNumArrayEntries();
      if (numArrayEntries != other.getNumArrayEntries()) {
        return entrySet().equals(other.entrySet());
      }
  
      for (int i = 0; i < numArrayEntries; i++) {
        if (!getArrayEntryAt(i).equals(other.getArrayEntryAt(i))) {
          return false;
        }
      }
  
      if (numArrayEntries != size) {
        return overflowEntries.equals(other.overflowEntries);
      }
  
  
      return true;
    }
  
    @Override
    public int hashCode() {
      int h = 0;
      final int listSize = getNumArrayEntries();
      for (int i = 0; i < listSize; i++) {
        h += entryList.get(i).hashCode();
      }
      // Avoid the iterator allocation if possible.
      if (getNumOverflowEntries() > 0) {
        h += overflowEntries.hashCode();
      }
      return h;
    }
  }
  